This invention relates to a rotary tool, such as a socket wrench or screwdriver, in which axial impact of a striker against an anvil member applies a rotational force to the anvil member in order to apply torque to a tool body associated with the anvil member. Such tools are useful in applications where it is necessary to augment the normal manual torque which can be applied by the tool, for example, in the removal of overtightened bolts, screws, nuts and the like.
Typically, in rotary impact tools of the above-type, an axial impact between the striker and anvil member applies a rotational force to the anvil member by means of complementary inclined striking surfaces formed on the striker and anvil member respectively, and commonly, oppositely handed sets of such surfaces are provided on the respective members so that rotary forces in either sense can be applied to the anvil member by suitably aligning the anvil member and striker to bring the relevant set of surfaces into engagement upon impact.
In one previously proposed rotary impact tool of the type described, the anvil member is fixed on the end of an elongate rod or shaft and the striker is rotatably and slidably mounted on the shaft above the anvil member. To obtain rotational movement of the anvil member when impacted by the striker, the striker is manually orientated on the shaft so as to mutually misalign the striking surfaces of the anvil member and striker and the striker is allowed to drop or is forcibly urged against the anvil member. With this arrangement, since the striker is freely rotatable on the shaft and is oriented manually by sight, it is possible that it may not accurately strike the anvil member in a manner producing optimum torque between the respective inclined surfaces and further, on impact, rotation may be induced in the striker rather than in the anvil member.
In another previously proposed tool, the anvil member is again fixed on the base of an elongate shaft, in this case of rectangular cross section, and the striker is oriented relative to the shaft by radial pins resiliently urged against the flat outer surfaces of the shaft. The striker can be rotated relative to the shaft, to change the direction of rotation imparted to the anvil member, by resilient movement of the pins, but with this arrangement, on impact of the striker against the anvil member, and rotation of the anvil member and shaft, the resilience in the connection between the striker and the shaft may tend to alter the orientation of the striker on the shaft which may again lead to inaccurate impacts which do not produce optimum torque.